In the AK47 and AKM family of semi-automatic Kalashnikov family of rifles the bolt carrier has a substantial mass. When it is blown back a substantial portion of its energy is absorbed by a long coiled spring. Any excess energy is dissipated on an impact area on the rear receiver of the gun. When the bolt carrier slides forward it is accelerated by the long coiled spring. All of its forward momentum is dissipated at the end of the forward stroke when it strikes and abruptly stops against the forward receiver post.
Others have recognized the need to cushion the impact between the steel bolt carrier and the steel receiver. Providing cushioning therebetween will quieten operation and extend the life of the gun. One solution has been to provide for a cushion insert positioned over the coiled spring, which extends downwardly immediately in front of the impact area on the rear receiver. While this protects the rear receiver, it does nothing to protect the smaller lug post on the forward receiver. Something is needed to protect the lug post and the bolt carrier when they strike each other.